چکیده انگلیسی

Abstract
The objective of this study was to evaluate the psychometric properties of the 20-item version of the Subjective Well-being Under Neuroleptic Treatment Scale (SWN) in patients, their siblings and parents and in healthy controls. In order to study heritability of subjective well-being, assessment in unaffected relatives and healthy controls is necessary. Data were obtained from the Dutch GROUP study (Genetic Risk and Outcome of Psychosis), a large cohort study on non-affective psychotic disorders incorporating patients, their relatives and healthy controls. The SWN scale and other relevant assessments were completed by 545 schizophrenia patients, 541 siblings, 75 parents, and 280 healthy controls. Reliability within the four groups ranged between Cronbach's alpha 0.88 and 0.92. Factor analysis indicated a single factor structure of the SWN scale, which makes only SWN total scores relevant.The WHO-Quality of Life psychological domain correlated highly with SWN total scores in all groups. Subclinical psychotic experiences were found to be associated with SWN total scores in relatives and healthy controls, supporting the psychosis continuum concept. The 20-item SWN scale is a reliable measure for subjective well-being that can also be used in relatives and healthy controls to investigate genetic and psychological dispositions of subjective well-being.

مقدمه انگلیسی

1. Introduction
Recent research has provided evidence that psychotic phenomena are distributed throughout the general population. The hypothesis of a ‘psychosis continuum’ was based on findings of odd convictions and attenuated psychotic experiences in general population samples. These psychotic experiences were traditionally only recognized in severe form in patients fulfilling criteria of schizophrenia spectrum diagnoses. Levels of subclinical psychotic phenomena were found to be higher in at-risk populations, such as relatives of schizophrenia patients and subjects using cannabis (Johns and van Os, 2001, Van Os et al., 2009, Van Os et al., 2010, Linscott and Van Os, 2010, Binbay et al., 2011 and Dominguez et al., 2011).
Based on this concept, it is relevant to investigate phenomena associated with schizophrenia in other populations, especially in relatives. One such related phenomenon is subjective wellbeing. Subjective wellbeing has been shown to be closely related to dopaminergic neuromodulation in the striatum (de Haan et al., 2000, de Haan et al., 2003 and Mizrahi et al., 2009). As all efficacious antipsychotic agents are dopamine antagonists, subjective well-being is influ-enced by antipsychotics, with higher dosage leading to a decrease in well- being. Subjective well-being of patients with schizophrenia is therefore relevant for medication adherence and recovery (Naber et al., 2001, Karow et al., 2007 and Lambert et al., 2007). Early improvement of subjective well-being after the start of treatment has been shown to predict better clinical outcome in the long term (Kluge et al., 2005, van Nimwegen et al., 2008, de Haan et al., 2008, Lambert et al., 2009, Mizrahi et al., 2009, Schennach-Wolff et al., 2010 and Kinon et al., 2010). Since subjective well-being is only moderately associated with psychopathology and clinicians' evaluation (Hunter and Barry, 2011, Karow et al., 2007, Karow et al., 2012, Chen et al., 2011 and Maurino et al., 2012), it is considered an independent outcome domain.
The Subjective Well-being Under Neuroleptic Treatment Scale (SWN, Naber et al., 1994 and Naber, 1995) is the most widely used self-rating scale in recent studies on subjective well-being in schizophrenia (Vothknecht et al., 2011). Originally, the SWN was developed to assess subjective experience in five subscales (Naber et al., 1994 and Naber et al., 2001). However, this subscale structure was not confirmed in later research (Siamouli et al., 2009 and Phillips et al., 2010). The psychometric properties are firmly established in schizophrenia patients (Naber, 1995, de Haan et al., 2002, Balestrieri et al., 2006 and Siamouli et al., 2009). The SWN has been shown to be sensitive to treatment adherence, medication change and remission (Naber, 1995, Naber et al., 2005 and de Haan et al., 2002). In neuroimaging studies the SWN was shown to be related to dopamine D2 receptor blockade. Several studies have demonstrated that a striatal dopamine D2 receptor occupancy between 60% and 70% correlates with positive subjective well-being of patients with schizophrenia. Higher occupancy of D2 receptors was associated with lower subjective well-being (de Haan et al., 2000, de Haan et al., 2003, Mizrahi et al., 2007 and Mizrahi et al., 2009). Therefore, a close relationship seems to exist between the psychological experience of subjective well-being as measured by the SWN and neurobiological mechanisms measured by differences in dopaminergic neurotransmission.
Although the importance of dopamine D2 receptor occupancy has been stressed in relation to psychosis and antipsychotic medication, D2 receptor density was also found to be associated with personality traits, attachment, social behavior and quality of life not only in patients with schizophrenia but also in healthy controls (Farde et al., 1997, Jönnson et al., 2003, Couture et al., 2007 and Cervenka et al., 2010).
Recently, research on genetic dispositions of emotional states has been expanded, e.g. by the GENEQOL consortium, a worldwide network to study genetic factors of quality of life (Sprangers et al., 2009 and Sprangers et al., 2010). From twin studies, the heritability of subjective well-being is estimated to be between 40% and 50% (Bartels and Boomsma, 2009). There is a large body of evidence indicating subjective well-being to be stable over the long term. This stability is mainly attributable to additive genetic factors, whereas susceptibility to change seems to be more related to temporary individual environmental factors (Nes et al., 2006). IIn a large study conducted by Bartels and Boomsma (2009), subjective well-being was assessed by measures of life satisfaction, happiness, quality of life and life fulfillment. They found that the four measures were explained by one underlying genetic factor. Therefore, distinct measures of subjective well-being are probably not distinct at a genetic level and represent overlapping constructs. They concluded that future research should focus on the complex interplay between genes and environment, regardless of which measure of subjective well-being is being used.
To determine hereditary aspects of subjective well-being and to facilitate future research into subjective well-being in non-clinicalsamples, the psychometric properties of the SWN scale in relatives of patients with psychotic disorders and in healthy controls need to be investigated.
Although the SWN was developed to address well-being under neuroleptic treatment in patients with psychosis (Naber et al., 1994, Naber, 1995 and de Haan et al., 2002), it can be used as an instrument to measure subjective well-being independent of treatment-specific aspects (Wolters et al., 2006 and Wolters et al., 2009a). It contains several items referring to subjective well-being in general. Although some items of the SWN may seem to apply to clinical populations, we hypothesized that we would find variations associated with subclinical psychotic phenomena and other subclinical psychopathology in non-clinical samples.
The content of the SWN was found to correlate highly with Quality of Life (QoL) scales (Wolters et al., 2006 and Wolters et al., 2009a). Therefore, we compared SWN measurements in non-clinical populations with the WHO-QoL Bref (The WHOQOL Group, 1998), a well-accepted standard of Quality of Life scales, as an indication of convergent validity.
1.1. Goal of the present study
The present study has two related objectives:
1.
To investigate and compare the psychometric properties of the SWN 20-item scale in patients, their unaffected relatives and healthy controls in terms of factor structure, internal consistency and reliability.
2.
To investigate the convergent validity of the SWN compared to the WHO-QoL Bref in patients, their unaffected relatives and healthy controls. We hypothesized that the SWN scale is a reliable and valid instrument for measuring subjective wellbeing in patients as well as in relatives and healthy controls.